Heretofore, a solid-state imaging device for synthesizing two image signals having the amount of exposure different from each other to obtain an image signal with a wide dynamic range is disclosed in, for example, the gazette of Japanese Laid-Open Patent No. HEI9-214829 and the gazette of Japanese Laid-Open Patent No. HEI9-275527.
The gazette of Japanese Laid-Open Patent No. HEI9-214829 discloses a digital still camera capable of obtaining an image signal with a wide dynamic range by level shifting two continuous field images picked up by the change of the exposure time, and then synthesizing them into one frame image.
The gazette of Japanese Laid-Open Patent No. HEI9-275527 discloses a digital still camera capable of obtaining an image signal with a wide dynamic range by level shifting a plurality of frame images having a different exposure times obtained from a plurality of CCDs, and then synthesizing them into one frame image.
In addition, there has been known an example of a video camera which expands the dynamic range by using a special CCD capable of reading a long-time exposure signal and a short-time exposure signal within one field period (“Development of method of processing single-plate Hyper-D color camera signal,” Image Media Society Technical Report, Vol. 22, No. 3, pp. 1-6 (1998)).
However, for example, in the digital still camera disclosed in the gazette of Japanese Laid-Open Patent No. HEI9-214829, two continuous field images picked up by the change of the exposure time are synthesized, so that the image after synthesized only has an image resolution for one field, that is, a resolution of a half of the number of pixels of CCD, whereby a short in the resolution of picked up image is concerned about.
On the other hand, in the digital still camera disclosed in the gazette of Japanese Laid-Open Patent No. HEI9-275527, image signals having a different exposure times picked up by a plurality of CCDs are synthesized, so that the image after synthesized has an image resolution for one frame, that is, a resolution for the number of pixels of CCD, and however, a plurality of CCDs are required, which is disadvantageous in the size/cost of the imaging device.
For the imaging device having been reported in “Development of method of processing single-plate Hyper-D color camera signal,” Image Media Society Technical Report, Vol. 22, No. 3, pp. 1-6 (1998), a special CCD is required to expand the dynamic range of picked up images.
It is an object of the present invention to provide a solid-state imaging device capable of picking up an image with an expanded dynamic range at a lower cost and at an image resolution equivalent to the number of pixels of CCD by using one CCD used generally with such a solid-state imaging device regardless of consumer or business applications.